Quick Fix

Sum your low end to mono below 80Hz using a Mid/Side EQ or a dedicated crossover tool, then check the mix in mono using your DAW's mono button before every bounce. If you lose kick and bass energy when you hit mono, you have phase cancellation below 200Hz that needs fixing now.

Most common cause: Stereo bass content below 80Hz causes destructive phase cancellation when the mix is summed to mono, wiping out the low end entirely on club systems, radio, and most phone speakers.

Your low end is disappearing in mono because you have stereo content below 80Hz that’s cancelling itself out when summed.

That sub-bass you spent two hours dialling in? On a club PA in mono, it’s either half the volume or completely gone. This is one of the most frustrating things that can happen to an otherwise finished mix. The fix is specific, and it’s faster than you think.

Why This Happens

Phase cancellation is the core issue. When two identical signals are 180 degrees out of phase and summed together, they cancel to silence. Your bass doesn’t need to be exactly 180 degrees out of phase to cause damage. Even 90 degrees of phase difference cuts low-end energy by up to 3dB.

Stereo bass content is the usual culprit. Chorus, flanger, or stereo widening on a bass track splits the signal into two slightly different versions. When a mono playback system sums those two versions together, the differences cancel.

Below 80Hz, the human ear can’t localise direction. Your brain registers bass frequencies as non-directional pressure. Stereo information down there isn’t contributing width. It’s only creating cancellation risk.

We had a mix come back from a mastering engineer once with a note that just said “check mono.” Hit the mono button, and the kick dropped 6dB. The bass guitar nearly vanished. The stereo widener on the bass bus was set to 100% width. That was it.

The Fix: Step by Step

Step 1: Hit the Mono Button Right Now

Every major DAW has one. In Ableton, it’s in the Master output section. In Logic, it’s the Dual Mono button on the output channel strip. In Pro Tools, fold to mono on your Monitor section. Hit it. If your low end drops more than 2dB, you have a problem. If it disappears, you have a severe problem.

Step 2: Find the Stereo Offenders

Solo your bass, kick, and sub layers individually, then hit mono for each. The track that collapses is your problem. Nine times out of ten it’s a bass track with a chorus, ensemble, or widening plugin sitting in the chain.

Step 3: Remove or Restrict Stereo Width Below 80Hz

Use a Mid/Side EQ to cut the Side channel below 80Hz. In Fabfilter Pro-Q 3, switch to M/S mode, click the Side channel, and add a low-cut at 80Hz with a 24dB per octave slope. That forces everything below 80Hz into mono while keeping your stereo width in the mids and highs.

If you’re using iZotope Ozone or a dedicated stereo imager, there’s usually a crossover control. Set the bass band to 0% width. It’s a satisfying fix because it’s surgical and you hear it immediately.

Step 4: Check Phase Between Kick and Bass

Load a free phase correlation meter. Look at the correlation between your kick and bass when they hit together. A reading below 0 means phase cancellation is happening. Flip the polarity on your bass track using the phase invert button (the circle with a line through it in most DAW channel strips) and check again. Sometimes that single click adds 4dB back to your low end.

Step 5: Use a Spectrum Analyser in Mono

Solo your master bus in mono and run a spectrum analyser like SPAN (free). Look at the 60Hz to 120Hz area. You should see a solid, consistent bump. If it’s notched or dipping, you’ve still got cancellation somewhere.

Step 6: High-Pass Unnecessary Tracks

Every track that isn’t your kick or bass should have a high-pass filter at 80Hz minimum. Guitars, pads, synth layers, and even room mics below 80Hz are cluttering the sub range and adding phase mess.

Step 7: Check Your Sub Layer Separately

If your bass has a separate sine wave sub layer, check the phase relationship between the sub and the bass fundamental. Misaligned sub layers are an ugly problem because they sound fine in stereo and completely hollow in mono.

If That Didn't Work

If you’ve done all of the above and the mono collapse is still happening, look at three other causes.

First, your room acoustics may be causing you to mix more bass than actually exists. What sounds balanced in your room vanishes when summed because the system you’re mixing on is hyping the low end.

Second, check your sample sources. Some bass presets and drum samples are bounced in stereo with phase issues already baked in. Load a mono instance and compare.

Third, a mid/side plugin earlier in your chain may be adding width below 80Hz without you realising.

How to Prevent This

Make mono checking part of your workflow, not an afterthought. We toggle mono three or four times during every mix session, starting from the first time kick and bass are in the same session together.

The rule is simple: keep everything below 80Hz in mono. Keep stereo content between 80Hz and 250Hz minimal. Let stereo width live above 250Hz where it actually does something useful for the listener.

Set a hard rule for yourself: no stereo wideners on the bass channel. Ever. Widen the upper harmonics if you need movement. Don’t widen the sub.

Related guides: Beginners guide to mixing

Frequently Asked Questions

What frequency should I keep in mono?

Everything below 80Hz should be mono in every mix. Many engineers push that up to 100Hz or even 120Hz for safety, especially if the track will play on club systems or broadcast. The wider you let that crossover point get, the more mono-compatible your mix becomes. We default to 80Hz as the minimum, not the maximum.

How do I check mono compatibility in my DAW?

Use your DAW's built-in mono button on the master output. In Ableton it's in the master track controls. In Logic it's the Dual Mono option. In Pro Tools use the monitoring section. Check it frequently during the mix, not just at the end. A track that sounds fine in stereo can have a serious mono problem you'd never catch without testing it directly.

Does phase cancellation only affect bass frequencies?

No, but it's most damaging in the low end because that's where music carries its energy and where playback systems diverge most dramatically between stereo and mono. Phase cancellation in the mid-range causes sounds to thin out or move in the stereo field. In the high end it affects air and shimmer. The bass version is the one that kills a mix fastest because it removes physical impact completely.